Generally, polycarbonate (PC) compositions exhibit properties such as high impact strength, flame retardancy and good transparency and for these reasons is the engineering resin of choice in electronic, appliance and automotive applications. Unfortunately, polycarbonate compositions have poor scratch resistance. One method of dealing with poor scratch resistance entails an expensive hard coating step in which a protective coating is applied to the surface of a PC article. Thus, a less expensive additive which could be blended with PC to produce a scratch resistant PC would be of commercial value.
Blends of polycarbonates and polymethyl methacrylate (co)polymers are known and have been investigated as a method of improving the scratch resistance of PC. Unfortunately, blends of PC and typical polymethyl methacrylates (PMMAs) are frequently opaque, which is not acceptable for semi-transparent or transparent applications, and they often suffer from poor mechanical properties.
Moreover, PC and PMMA are immiscible in most proportions, and blends thereof are opaque over wide composition ranges and do not possess the advantageous properties exhibited by either polymer.
Techniques of overcoming the drawbacks associated with the immiscibility of typical PC/PMMA blends have been previously proposed. Among such techniques is the addition of copolymer additives, such as PMMA/acrylamide copolymers and PMMA-ester copolymers containing carbocyclic groups and the use of a block copolymer of PC and PMMA instead of a physical mixture of the two components.
A need exists for a modified PC composition, having an increase of three to four levels of hardness on the pencil hardness scale over the unmodified PC composition, that eliminates the need for a hard coating step.